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NAEP Analysis and Scaling → Estimation of Population and Student Group Distributions → Examining the Population-Structure Models Used in NAEP → Proportion of Variance Accounted for By Principal Components Used in NAEP Population-Structure Models → Proportion of Variance of the Group-Defining Contrasts Accounted for by the Principal Components Used in the Population-Structure Model, Grade 12 Writing National Main Assessment: 2007

NAEP Technical DocumentationProportion of variance of the group-defining contrasts accounted for by the principal components used in the population-structure model, grade 12 writing national main assessment: 2007

Type of contrast	Number of contrasts	Mean	Minimum	Maximum	Number of contrasts by proportion1 of variance explained
					0.00 - 0.70	0.70 - 0.80	0.80 - 0.90	0.90 - 0.95	0.95 - 1.00
1 (Total Variance – Residual Variance)/Total Variance, where Total Variance consists of both sampling and measurement error variance. NOTE: SD/ELL = Students with disabilities/English language learners. SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2007 Writing Assessment.
All contrasts	930	0.90	0.58	0.99	16	45	346	269	254
Student questionnaire	197	0.90	0.58	0.99	3	8	74	68	44
Major reporting variables	69	0.90	0.72	0.99	0	8	29	5	27
Interactions between reporting variables	481	0.91	0.63	0.99	13	19	123	156	170
School questionnaire	146	0.87	0.76	0.98	0	6	107	29	4
SD/ELL questionnaire	37	0.90	0.77	0.98	0	4	13	11	9

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